With ensure_ascii, the view's dump wrote every string through the escaping
path, which decodes UTF-8 byte by byte, even strings of the source that are
plain ASCII. A string of the source without escape sequences has no quote,
backslash, or control character, so ensure_ascii leaves it unchanged
exactly when it has no byte >= 0x7F. The dump now checks that eight bytes
at a time (one add and one or per word) and copies such strings like the
dump without ensure_ascii.
The compact walk (dump_compact) now also serves ensure_ascii, through a
separate out-of-line instantiation, so the walk without ensure_ascii keeps
its speed.
Parsing is unchanged. A flag set by the parser would let the dump skip the
check and was about twice as fast for compact output, but it costs every
parse of string-heavy input 1-2% with GCC.
Signed-off-by: Niels Lohmann <mail@nlohmann.me>
Niels Lohmann
7c26e99ac5